The subpopulations of neurons in the cat retina which utilize specific chemical neurotransmitters are being investigated by autoradiographic and other cytochemical techniques. Serial section autoradiography is being utilized to provide a basis for both light and electron microscopic reconstruction of neuronal populations which exhibit preferential accumulation of 3H-glycine, GABA, taurine, and -dopamine. Peroxidase-conjugated alpha-bungarotoxin is being used for identification of neurons involved in transmission of acetylcholine to nicotinic receptors. The effects of light vs. dark adaptation and of specific wave length stimulation are also being investigated.